The National Bariatric Surgery Registry has revealed that nearly 40% of under-25s who have weight-loss surgery in the UK are classified as super-obese, resulting in costs that threaten to cripple the NHS.

The group of surgeons, which looked at 18,000 weight-loss operations in 137 UK hospitals between 2010 and 2013, said that overall more Britons are having the procedure, blighted by illness that accompanies being chronically overweight.

Out of the 9,526 gastric bypass procedures, 4,705 gastric band operations and 3,797 sleeve gastrectomy operations were analysed: 550 young people under the age of 25 had weight loss surgery of some kind, while 62 were under 18.

"In particular, the effect on diabetes has important implications for the NHS. Bariatric surgery cost-effectively improves the health of obese patients," said Mr Richard Welbourn, consultant surgeon and chairman of the National Bariatric Surgery Registry.

Severe and complex obesity and the associated illnesses that come with it means it is a condition "which threatened to bankrupt the NHS".

A separate study recently published in the Lancet Diabetes and Endocrinology journal said bariatric surgery could be the key in saving NHS billions of pounds a year, as it is found to have dramatically reduced the chance of developing type 2 diabetes.

Type 2 diabetes leaves a person unable to control their blood sugar levels and can result in blindness, amputations and nerve damage.

Government figures show that type 2 diabetes, which is closely linked to being overweight, costs the NHS over £1.5m (€1.9m, $2.4m) an hour, or 10% of the NHS budget for England and Wales.

This equates to over £25,000 being spent on diabetes every minute and estimated £14bn each year on treating diabetes and its complications.

Around 3% of morbidly obese people develop type 2 diabetes each year.

Meanwhile, the Centre for Economic and Business Research warned Britain that the country faces a whopping £18.4bn in costs related to heart disease by 2020.

Those who are overweight are also more likely to develop heart disease as well.